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Integration of temporal and spatial patterning generates neural diversity. Nature 2017; 541:365-370. [PMID: 28077877 DOI: 10.1038/nature20794] [Citation(s) in RCA: 83] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2015] [Accepted: 11/16/2016] [Indexed: 12/27/2022]
Abstract
In the Drosophila optic lobes, 800 retinotopically organized columns in the medulla act as functional units for processing visual information. The medulla contains over 80 types of neuron, which belong to two classes: uni-columnar neurons have a stoichiometry of one per column, while multi-columnar neurons contact multiple columns. Here we show that combinatorial inputs from temporal and spatial axes generate this neuronal diversity: all neuroblasts switch fates over time to produce different neurons; the neuroepithelium that generates neuroblasts is also subdivided into six compartments by the expression of specific factors. Uni-columnar neurons are produced in all spatial compartments independently of spatial input; they innervate the neuropil where they are generated. Multi-columnar neurons are generated in smaller numbers in restricted compartments and require spatial input; the majority of their cell bodies subsequently move to cover the entire medulla. The selective integration of spatial inputs by a fixed temporal neuroblast cascade thus acts as a powerful mechanism for generating neural diversity, regulating stoichiometry and the formation of retinotopy.
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Copenhaver PF, Ramaker JM. Neuronal migration during development and the amyloid precursor protein. CURRENT OPINION IN INSECT SCIENCE 2016; 18:1-10. [PMID: 27939704 PMCID: PMC5157842 DOI: 10.1016/j.cois.2016.08.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2016] [Accepted: 08/06/2016] [Indexed: 06/06/2023]
Abstract
The Amyloid Precursor Protein (APP) is the source of amyloid peptides that accumulate in Alzheimer's disease. However, members of the APP family are strongly expressed in the developing nervous systems of invertebrates and vertebrates, where they regulate neuronal guidance, synaptic remodeling, and injury responses. In contrast to mammals, insects express only one APP ortholog (APPL), simplifying investigations into its normal functions. Recent studies have shown that APPL regulates neuronal migration in the developing insect nervous system, analogous to the roles ascribed to APP family proteins in the mammalian cortex. The comparative simplicity of insect systems offers new opportunities for deciphering the signaling mechanisms by which this enigmatic class of proteins contributes to the formation and function of the nervous system.
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Affiliation(s)
- Philip F Copenhaver
- Department of Cell, Developmental and Cancer Biology, Oregon Health & Science University, Portland, OR 97239, USA.
| | - Jenna M Ramaker
- Department of Cell, Developmental and Cancer Biology, Oregon Health & Science University, Portland, OR 97239, USA; Department of Pathology, Oregon Health & Science University, Portland, OR 97239, USA
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53
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Suzuki T, Trush O, Yasugi T, Takayama R, Sato M. Wnt Signaling Specifies Anteroposterior Progenitor Zone Identity in the Drosophila Visual Center. J Neurosci 2016; 36:6503-13. [PMID: 27307238 PMCID: PMC6601925 DOI: 10.1523/jneurosci.0864-16.2016] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2016] [Revised: 04/26/2016] [Accepted: 05/09/2016] [Indexed: 02/06/2023] Open
Abstract
UNLABELLED During brain development, various types of neuronal populations are produced from different progenitor pools to produce neuronal diversity that is sufficient to establish functional neuronal circuits. However, the molecular mechanisms that specify the identity of each progenitor pool remain obscure. Here, we show that Wnt signaling is essential for the specification of the identity of posterior progenitor pools in the Drosophila visual center. In the medulla, the largest component of the visual center, different types of neurons are produced from two progenitor pools: the outer proliferation center (OPC) and glial precursor cells (GPCs; also known as tips of the OPC). We found that OPC-type neurons are produced from the GPCs at the expense of GPC-type neurons when Wnt signaling is suppressed in the GPCs. In contrast, GPC-type neurons are ectopically induced when Wnt signaling is ectopically activated in the OPC. These results suggest that Wnt signaling is necessary and sufficient for the specification of the progenitor pool identity. We also found that Homothorax (Hth), which is temporally expressed in the OPC, is ectopically induced in the GPCs by suppression of Wnt signaling and that ectopic induction of Hth phenocopies the suppression of Wnt signaling in the GPCs. Thus, Wnt signaling is involved in regionalization of the fly visual center through the specification of the progenitor pool located posterior to the medulla by suppressing Hth expression. SIGNIFICANCE STATEMENT Brain consists of considerably diverse neurons of different origins. In mammalian brain, excitatory and inhibitory neurons derive from the dorsal and ventral telencephalon, respectively. Multiple progenitor pools also contribute to the neuronal diversity in fly brain. However, it has been unclear how differences between these progenitor pools are established. Here, we show that Wnt signaling, an evolutionarily conserved signaling, is involved in the process that establishes the differences between these progenitor pools. Because β-catenin signaling, which is under the control of Wnt ligands, specifies progenitor pool identity in the developing mammalian thalamus, Wnt signaling-mediated specification of progenitor pool identity may be conserved in insect and mammalian brains.
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Affiliation(s)
- Takumi Suzuki
- Laboratory of Developmental Neurobiology, Brain/Liver Interface Medicine Research Center
| | | | - Tetsuo Yasugi
- Mathematical Neuroscience Unit, Institute for Frontier Science Initiative, Kanazawa University, Ishikawa 920-8640, Japan, and
| | - Rie Takayama
- Mathematical Neuroscience Unit, Institute for Frontier Science Initiative, Kanazawa University, Ishikawa 920-8640, Japan, and Core Research for Evolutional Science and Technology, JST, Saitama 332-0012, Japan
| | - Makoto Sato
- Laboratory of Developmental Neurobiology, Brain/Liver Interface Medicine Research Center, Graduate School of Medical Sciences, and Mathematical Neuroscience Unit, Institute for Frontier Science Initiative, Kanazawa University, Ishikawa 920-8640, Japan, and Core Research for Evolutional Science and Technology, JST, Saitama 332-0012, Japan
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54
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A Unique Class of Neural Progenitors in the Drosophila Optic Lobe Generates Both Migrating Neurons and Glia. Cell Rep 2016; 15:774-786. [PMID: 27149843 PMCID: PMC5154769 DOI: 10.1016/j.celrep.2016.03.061] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2015] [Revised: 01/25/2016] [Accepted: 03/15/2016] [Indexed: 02/04/2023] Open
Abstract
How neuronal and glial fates are specified from neural precursor cells is an important question for developmental neurobiologists. We address this question in the Drosophila optic lobe, composed of the lamina, medulla, and lobula complex. We show that two gliogenic regions posterior to the prospective lamina also produce lamina wide-field (Lawf) neurons, which share common progenitors with lamina glia. These progenitors express neither canonical neuroblast nor lamina precursor cell markers. They bifurcate into two sub-lineages in response to Notch signaling, generating lamina glia or Lawf neurons, respectively. The newly born glia and Lawfs then migrate tangentially over substantial distances to reach their target tissue. Thus, Lawf neurogenesis, which includes a common origin with glia, as well as neuronal migration, resembles several aspects of vertebrate neurogenesis.
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55
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Suzuki T, Hasegawa E, Nakai Y, Kaido M, Takayama R, Sato M. Formation of Neuronal Circuits by Interactions between Neuronal Populations Derived from Different Origins in the Drosophila Visual Center. Cell Rep 2016; 15:499-509. [PMID: 27068458 DOI: 10.1016/j.celrep.2016.03.056] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2015] [Revised: 01/14/2016] [Accepted: 03/15/2016] [Indexed: 11/28/2022] Open
Abstract
A wide variety of neurons, including populations derived from different origins, are precisely arranged and correctly connected with their partner to establish a functional neural circuit during brain development. The molecular mechanisms that orchestrate the production and arrangement of these neurons have been obscure. Here, we demonstrate that cell-cell interactions play an important role in establishing the arrangement of neurons of different origins in the Drosophila visual center. Specific types of neurons born outside the medulla primordium migrate tangentially into the developing medulla cortex. During their tangential migration, these neurons express the repellent ligand Slit, and the two layers that the neurons intercalate between express the receptors Robo2 and Robo3. Genetic analysis suggests that Slit-Robo signaling may control the positioning of the layer cells or their processes to form a path for migration. Our results suggest that conserved axon guidance signaling is involved in the interactions between neurons of different origins during brain development.
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Affiliation(s)
- Takumi Suzuki
- Brain/Liver Interface Medicine Research Center, Kanazawa University, 13-1 Takaramachi, Kanazawa, Ishikawa 920-8640, Japan
| | - Eri Hasegawa
- Brain/Liver Interface Medicine Research Center, Kanazawa University, 13-1 Takaramachi, Kanazawa, Ishikawa 920-8640, Japan
| | - Yasuhiro Nakai
- Brain/Liver Interface Medicine Research Center, Kanazawa University, 13-1 Takaramachi, Kanazawa, Ishikawa 920-8640, Japan; CREST, JST, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
| | - Masako Kaido
- Brain/Liver Interface Medicine Research Center, Kanazawa University, 13-1 Takaramachi, Kanazawa, Ishikawa 920-8640, Japan
| | - Rie Takayama
- Brain/Liver Interface Medicine Research Center, Kanazawa University, 13-1 Takaramachi, Kanazawa, Ishikawa 920-8640, Japan; CREST, JST, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
| | - Makoto Sato
- Brain/Liver Interface Medicine Research Center, Kanazawa University, 13-1 Takaramachi, Kanazawa, Ishikawa 920-8640, Japan; Mathematical Neuroscience Unit, Institute for Frontier Science Initiative, Kanazawa University, 13-1 Takaramachi, Kanazawa, Ishikawa 920-8640, Japan; Laboratory of Developmental Neurobiology, Graduate School of Medical Sciences, Kanazawa University, 13-1 Takaramachi, Kanazawa, Ishikawa 920-8640, Japan; CREST, JST, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan.
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56
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Kulkarni A, Ertekin D, Lee CH, Hummel T. Birth order dependent growth cone segregation determines synaptic layer identity in the Drosophila visual system. eLife 2016; 5:e13715. [PMID: 26987017 PMCID: PMC4846375 DOI: 10.7554/elife.13715] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2015] [Accepted: 03/16/2016] [Indexed: 12/13/2022] Open
Abstract
The precise recognition of appropriate synaptic partner neurons is a critical step during neural circuit assembly. However, little is known about the developmental context in which recognition specificity is important to establish synaptic contacts. We show that in the Drosophila visual system, sequential segregation of photoreceptor afferents, reflecting their birth order, lead to differential positioning of their growth cones in the early target region. By combining loss- and gain-of-function analyses we demonstrate that relative differences in the expression of the transcription factor Sequoia regulate R cell growth cone segregation. This initial growth cone positioning is consolidated via cell-adhesion molecule Capricious in R8 axons. Further, we show that the initial growth cone positioning determines synaptic layer selection through proximity-based axon-target interactions. Taken together, we demonstrate that birth order dependent pre-patterning of afferent growth cones is an essential pre-requisite for the identification of synaptic partner neurons during visual map formation in Drosophila. DOI:http://dx.doi.org/10.7554/eLife.13715.001 A nervous system requires a precise network of connections between cells called neurons to work properly. Within the brain, the fiber-like connections between pairs of neurons are not running crisscross like a pile of spaghetti. Instead, connected partner neurons are organized into distinct layers and columns. Many questions remain about how these partner neurons find each other and how the layers of fiber-like connections form. To answer these questions, scientists often study the part of the fruit fly nervous system that controls the insect’s vision. This brain-like structure is simple and can be easily manipulated with genetic engineering. Fruit fly studies have helped identify some molecules that play a role in helping partner cells find one another and connect. These studies have also shown that the timing of brain cell development appears to play a role. But the role that layer formation plays in the process is still a mystery. Now, Kulkarni et al. show that the birthdate of neurons in the fruit fly visual system helps organize them into layers. These neurons are generated early in the development of the fly. Shortly after birth, a molecular clock under the control of a protein called Sequoia starts within each newly generated neuron. The Sequoia protein is a transcription factor and controls the activity of many genes, and the molecular clock provides the growing neuron fibers with information about where and when to look for its partner neurons. By manipulating the amount and time that Sequoia is produced in the fly visual system, Kulkarni et al. show that this clock helps arrange the growing cells into layers. Cells with similar birthdates connect and are arranged into layers. How much and when Sequoia is produced dictates where each new layer begins. The next steps for the research will be to learn more about how the clock works and identify any intermediaries between the clock and cell growth patterns. DOI:http://dx.doi.org/10.7554/eLife.13715.002
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Affiliation(s)
| | - Deniz Ertekin
- Department of Neurobiology, University of Vienna, Vienna, Austria
| | - Chi-Hon Lee
- Section on Neuronal Connectivity, Laboratory of Gene Regulation and Development, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, United States
| | - Thomas Hummel
- Department of Neurobiology, University of Vienna, Vienna, Austria
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57
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Super-Resolution Mapping of Neuronal Circuitry With an Index-Optimized Clearing Agent. Cell Rep 2016; 14:2718-32. [DOI: 10.1016/j.celrep.2016.02.057] [Citation(s) in RCA: 178] [Impact Index Per Article: 22.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2015] [Revised: 01/11/2016] [Accepted: 02/09/2016] [Indexed: 11/18/2022] Open
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58
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Suzuki T, Takayama R, Sato M. eyeless/Pax6 controls the production of glial cells in the visual center of Drosophila melanogaster. Dev Biol 2015; 409:343-53. [PMID: 26670857 DOI: 10.1016/j.ydbio.2015.12.004] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2015] [Revised: 11/11/2015] [Accepted: 12/04/2015] [Indexed: 10/22/2022]
Abstract
Pax6 is known as a neurogenic factor in the development of the central nervous system and regulates proliferation of neuronal progenitor cells and promotes neuronal differentiation. In addition to neurogenesis, Pax6 is also involved in the specification and maturation of glial cells. Here, we show that Eyeless (Ey), Drosophila homolog of Pax6, regulates the production of glial cells in the brain. In the developing fly visual center, the production of neurons and glial cells are controlled by the temporal transcription factors that are sequentially expressed in neuroblasts (NBs). Among them, NBs of the last temporal window produce astrocyte-like glial cells. Ey is strongly expressed in the middle aged NBs, whose temporal window is earlier compared with glia producing older NBs. Weak Ey expression is also detected in the glia producing NBs. Our results suggest that Ey expression in the middle aged NBs indirectly control gliogenesis from the oldest NBs by regulating other temporal transcription factors. Additionally, weak Ey expression in the NBs of last temporal window may directly control gliogenesis. Ey is also expressed in neurons produced from the NBs of Ey-positive temporal window. Interestingly, neuron-specific overexpression of Ey causes significant increase in glial cells suggesting that neuronal expression of Ey may also contribute to gliogenesis. Thus, Pax6-dependent regulation of astrocyte-like glial development is conserved throughout the animal kingdom.
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Affiliation(s)
- Takumi Suzuki
- Laboratory of Developmental Neurobiology, Brain/Liver Interface Medicine Research Center, Kanazawa University, 13-1 Takaramachi Kanazawa-shi, Ishikawa 920-8640, Japan
| | - Rie Takayama
- Laboratory of Developmental Neurobiology, Brain/Liver Interface Medicine Research Center, Kanazawa University, 13-1 Takaramachi Kanazawa-shi, Ishikawa 920-8640, Japan; CREST, JST, 4-1-8 Honcho Kawaguchi, Saitama 332-0012, Japan
| | - Makoto Sato
- Laboratory of Developmental Neurobiology, Brain/Liver Interface Medicine Research Center, Kanazawa University, 13-1 Takaramachi Kanazawa-shi, Ishikawa 920-8640, Japan; Graduate School of Medical Sciences, Kanazawa University, 13-1 Takaramachi Kanazawa-shi, Ishikawa 920-8640, Japan; CREST, JST, 4-1-8 Honcho Kawaguchi, Saitama 332-0012, Japan.
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59
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Ammer G, Leonhardt A, Bahl A, Dickson BJ, Borst A. Functional Specialization of Neural Input Elements to the Drosophila ON Motion Detector. Curr Biol 2015; 25:2247-53. [PMID: 26234212 DOI: 10.1016/j.cub.2015.07.014] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2015] [Revised: 07/01/2015] [Accepted: 07/02/2015] [Indexed: 10/23/2022]
Abstract
Detecting the direction of visual movement is fundamental for every sighted animal in order to navigate, avoid predators, or detect conspecifics. Algorithmic models of correlation-type motion detectors describe the underlying computation remarkably well. They consist of two spatially separated input lines that are asymmetrically filtered in time and then interact in a nonlinear way. However, the cellular implementation of this computation remains elusive. Recent connectomic data of the Drosophila optic lobe has suggested a neural circuit for the detection of moving bright edges (ON motion) with medulla cells Mi1 and Tm3 providing spatially offset input to direction-selective T4 cells, thereby forming the two input lines of a motion detector. Electrophysiological characterization of Mi1 and Tm3 revealed different temporal filtering properties and proposed them to correspond to the delayed and direct input, respectively. Here, we test this hypothesis by silencing either Mi1 or Tm3 cells and using electrophysiological recordings and behavioral responses of flies as a readout. We show that Mi1 is a necessary element of the ON pathway under all stimulus conditions. In contrast, Tm3 is specifically required only for the detection of fast ON motion in the preferred direction. We thereby provide first functional evidence that Mi1 and Tm3 are key elements of the ON pathway and uncover an unexpected functional specialization of these two cell types. Our results thus require an elaboration of the currently prevailing model for ON motion detection and highlight the importance of functional studies for neural circuit breaking.
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Affiliation(s)
- Georg Ammer
- Max Planck Institute of Neurobiology, Am Klopferspitz 18, 82152 Martinsried, Germany.
| | - Aljoscha Leonhardt
- Max Planck Institute of Neurobiology, Am Klopferspitz 18, 82152 Martinsried, Germany
| | - Armin Bahl
- Max Planck Institute of Neurobiology, Am Klopferspitz 18, 82152 Martinsried, Germany
| | - Barry J Dickson
- Janelia Research Campus, Howard Hughes Medical Institute, 19700 Helix Drive, Ashburn, VA 20147, USA
| | - Alexander Borst
- Max Planck Institute of Neurobiology, Am Klopferspitz 18, 82152 Martinsried, Germany.
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60
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Shinomiya K, Takemura SY, Rivlin PK, Plaza SM, Scheffer LK, Meinertzhagen IA. A common evolutionary origin for the ON- and OFF-edge motion detection pathways of the Drosophila visual system. Front Neural Circuits 2015. [PMID: 26217193 PMCID: PMC4496578 DOI: 10.3389/fncir.2015.00033] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Synaptic circuits for identified behaviors in the Drosophila brain have typically been considered from either a developmental or functional perspective without reference to how the circuits might have been inherited from ancestral forms. For example, two candidate pathways for ON- and OFF-edge motion detection in the visual system act via circuits that use respectively either T4 or T5, two cell types of the fourth neuropil, or lobula plate (LOP), that exhibit narrow-field direction-selective responses and provide input to wide-field tangential neurons. T4 or T5 both have four subtypes that terminate one each in the four strata of the LOP. Representatives are reported in a wide range of Diptera, and both cell types exhibit various similarities in: (1) the morphology of their dendritic arbors; (2) their four morphological and functional subtypes; (3) their cholinergic profile in Drosophila; (4) their input from the pathways of L3 cells in the first neuropil, or lamina (LA), and by one of a pair of LA cells, L1 (to the T4 pathway) and L2 (to the T5 pathway); and (5) their innervation by a single, wide-field contralateral tangential neuron from the central brain. Progenitors of both also express the gene atonal early in their proliferation from the inner anlage of the developing optic lobe, being alone among many other cell type progeny to do so. Yet T4 receives input in the second neuropil, or medulla (ME), and T5 in the third neuropil or lobula (LO). Here we suggest that these two cell types were originally one, that their ancestral cell population duplicated and split to innervate separate ME and LO neuropils, and that a fiber crossing—the internal chiasma—arose between the two neuropils. The split most plausibly occurred, we suggest, with the formation of the LO as a new neuropil that formed when it separated from its ancestral neuropil to leave the ME, suggesting additionally that ME input neurons to T4 and T5 may also have had a common origin.
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Affiliation(s)
- Kazunori Shinomiya
- Department of Psychology and Neuroscience, Life Sciences Centre, Dalhousie University Halifax, NS, Canada ; FlyEM Project Team, Howard Hughes Medical Institute, Janelia Research Campus Ashburn, VA, USA
| | - Shin-ya Takemura
- FlyEM Project Team, Howard Hughes Medical Institute, Janelia Research Campus Ashburn, VA, USA
| | - Patricia K Rivlin
- FlyEM Project Team, Howard Hughes Medical Institute, Janelia Research Campus Ashburn, VA, USA
| | - Stephen M Plaza
- FlyEM Project Team, Howard Hughes Medical Institute, Janelia Research Campus Ashburn, VA, USA
| | - Louis K Scheffer
- FlyEM Project Team, Howard Hughes Medical Institute, Janelia Research Campus Ashburn, VA, USA
| | - Ian A Meinertzhagen
- Department of Psychology and Neuroscience, Life Sciences Centre, Dalhousie University Halifax, NS, Canada ; Department of Biology, Life Sciences Centre, Dalhousie University Halifax, NS, Canada
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61
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Optimized tools for multicolor stochastic labeling reveal diverse stereotyped cell arrangements in the fly visual system. Proc Natl Acad Sci U S A 2015; 112:E2967-76. [PMID: 25964354 DOI: 10.1073/pnas.1506763112] [Citation(s) in RCA: 328] [Impact Index Per Article: 36.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We describe the development and application of methods for high-throughput neuroanatomy in Drosophila using light microscopy. These tools enable efficient multicolor stochastic labeling of neurons at both low and high densities. Expression of multiple membrane-targeted and distinct epitope-tagged proteins is controlled both by a transcriptional driver and by stochastic, recombinase-mediated excision of transcription-terminating cassettes. This MultiColor FlpOut (MCFO) approach can be used to reveal cell shapes and relative cell positions and to track the progeny of precursor cells through development. Using two different recombinases, the number of cells labeled and the number of color combinations observed in those cells can be controlled separately. We demonstrate the utility of MCFO in a detailed study of diversity and variability of Distal medulla (Dm) neurons, multicolumnar local interneurons in the adult visual system. Similar to many brain regions, the medulla has a repetitive columnar structure that supports parallel information processing together with orthogonal layers of cell processes that enable communication between columns. We find that, within a medulla layer, processes of the cells of a given Dm neuron type form distinct patterns that reflect both the morphology of individual cells and the relative positions of their arbors. These stereotyped cell arrangements differ between cell types and can even differ for the processes of the same cell type in different medulla layers. This unexpected diversity of coverage patterns provides multiple independent ways of integrating visual information across the retinotopic columns and implies the existence of multiple developmental mechanisms that generate these distinct patterns.
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62
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Wernet MF, Huberman AD, Desplan C. So many pieces, one puzzle: cell type specification and visual circuitry in flies and mice. Genes Dev 2014; 28:2565-84. [PMID: 25452270 PMCID: PMC4248288 DOI: 10.1101/gad.248245.114] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
The visual system is a powerful model for probing the development, connectivity, and function of neural circuits. Two genetically tractable species, mice and flies, are together providing a great deal of understanding of these processes. Current efforts focus on integrating knowledge gained from three cross-fostering fields of research: (1) understanding how the fates of different cell types are specified during development, (2) revealing the synaptic connections between identified cell types ("connectomics") by high-resolution three-dimensional circuit anatomy, and (3) causal testing of how identified circuit elements contribute to visual perception and behavior. Here we discuss representative examples from fly and mouse models to illustrate the ongoing success of this tripartite strategy, focusing on the ways it is enhancing our understanding of visual processing and other sensory systems.
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Affiliation(s)
- Mathias F Wernet
- Department of Neurobiology, Stanford University, Stanford, California 94305, USA; New York University Abu Dhabi, Saadiyat Island, Abu Dhabi 129188, United Arab Emirates; Department of Biology, New York University, New York, New York 10003, USA
| | - Andrew D Huberman
- Department of Neurosciences, Neurobiology Section, Division of Biological Sciences, University of California at San Diego, La Jolla, California 92093, USA
| | - Claude Desplan
- New York University Abu Dhabi, Saadiyat Island, Abu Dhabi 129188, United Arab Emirates; Department of Biology, New York University, New York, New York 10003, USA
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63
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Suzuki T, Sato M. Neurogenesis and neuronal circuit formation in the Drosophila visual center. Dev Growth Differ 2014; 56:491-8. [PMID: 25200311 DOI: 10.1111/dgd.12151] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2014] [Revised: 06/23/2014] [Accepted: 06/26/2014] [Indexed: 11/24/2022]
Abstract
The Drosophila optic lobe is composed of a wide variety of neurons that form laminar structures and columnar units. The fly optic lobe shares structural features with the mammalian brain, and fly genetics allow precise genetic manipulations. Thus, the Drosophila visual center is an excellent model for studying the mechanisms underlying the establishment of a functional neuronal circuit during brain development. However, little is understood about the developmental mechanisms that produce neuronal diversity and establish neuronal circuits in the medulla, the largest component of the optic lobe. Our recent research revealed key features of medulla development, such as birth-order-dependent specification of neuronal types and the subdivision of the medulla primordium into concentric zones, which is characterized by the expression of four transcription factors. Here, we review recent investigations into the development of the medulla and discuss the mechanisms that establish functional neuronal circuits.
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Affiliation(s)
- Takumi Suzuki
- Laboratory of Developmental Neurobiology, Brain/Liver Interface Medicine Research Center, Kanazawa University, 13-1 Takaramachi, Kanazawa, Ishikawa, 920-8640, Japan
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64
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Lah GJE, Li JSS, Millard SS. Cell-specific alternative splicing of Drosophila Dscam2 is crucial for proper neuronal wiring. Neuron 2014; 83:1376-88. [PMID: 25175881 DOI: 10.1016/j.neuron.2014.08.002] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/24/2014] [Indexed: 01/11/2023]
Abstract
How a finite number of genes specify a seemingly infinite number of neuronal connections is a central question in neurobiology. Alternative splicing has been proposed to increase proteome diversity in the brain. Here we show that cell-specific alternative splicing of a cell-surface protein is crucial for neuronal wiring. Down syndrome cell adhesion molecule 2 (Dscam2) is a conserved homophilic binding protein that can induce repulsion between opposing neurons. In the fly visual system, L1 and L2 neurons both require Dscam2 repulsion, but paradoxically, they also physically contact each other. We found that the cell-specific expression of two biochemically distinct alternative isoforms of Dscam2 prevents these cells from repelling each other. Phenotypes were observed in the axon terminals of L1 and L2 when they expressed the incorrect isoform, demonstrating a requirement for distinct isoforms. We conclude that cell-specific alternative splicing is a mechanism for achieving proper connectivity between neurons.
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Affiliation(s)
- Grace Ji-Eun Lah
- School of Biomedical Sciences, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Joshua Shing Shun Li
- School of Biomedical Sciences, The University of Queensland, Brisbane, QLD 4072, Australia
| | - S Sean Millard
- School of Biomedical Sciences, The University of Queensland, Brisbane, QLD 4072, Australia.
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65
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Apitz H, Salecker I. A Challenge of Numbers and Diversity: Neurogenesis in theDrosophilaOptic Lobe. J Neurogenet 2014; 28:233-49. [DOI: 10.3109/01677063.2014.922558] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
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66
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Processing properties of ON and OFF pathways for Drosophila motion detection. Nature 2014; 512:427-30. [PMID: 25043016 DOI: 10.1038/nature13427] [Citation(s) in RCA: 153] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2013] [Accepted: 05/01/2014] [Indexed: 12/18/2022]
Abstract
The algorithms and neural circuits that process spatio-temporal changes in luminance to extract visual motion cues have been the focus of intense research. An influential model, the Hassenstein-Reichardt correlator, relies on differential temporal filtering of two spatially separated input channels, delaying one input signal with respect to the other. Motion in a particular direction causes these delayed and non-delayed luminance signals to arrive simultaneously at a subsequent processing step in the brain; these signals are then nonlinearly amplified to produce a direction-selective response. Recent work in Drosophila has identified two parallel pathways that selectively respond to either moving light or dark edges. Each of these pathways requires two critical processing steps to be applied to incoming signals: differential delay between the spatial input channels, and distinct processing of brightness increment and decrement signals. Here we demonstrate, using in vivo patch-clamp recordings, that four medulla neurons implement these two processing steps. The neurons Mi1 and Tm3 respond selectively to brightness increments, with the response of Mi1 delayed relative to Tm3. Conversely, Tm1 and Tm2 respond selectively to brightness decrements, with the response of Tm1 delayed compared with Tm2. Remarkably, constraining Hassenstein-Reichardt correlator models using these measurements produces outputs consistent with previously measured properties of motion detectors, including temporal frequency tuning and specificity for light versus dark edges. We propose that Mi1 and Tm3 perform critical processing of the delayed and non-delayed input channels of the correlator responsible for the detection of light edges, while Tm1 and Tm2 play analogous roles in the detection of moving dark edges. Our data show that specific medulla neurons possess response properties that allow them to implement the algorithmic steps that precede the correlative operation in the Hassenstein-Reichardt correlator, revealing elements of the long-sought neural substrates of motion detection in the fly.
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67
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Danielsen ET, Moeller ME, Dorry E, Komura-Kawa T, Fujimoto Y, Troelsen JT, Herder R, O'Connor MB, Niwa R, Rewitz KF. Transcriptional control of steroid biosynthesis genes in the Drosophila prothoracic gland by ventral veins lacking and knirps. PLoS Genet 2014; 10:e1004343. [PMID: 24945799 PMCID: PMC4063667 DOI: 10.1371/journal.pgen.1004343] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2013] [Accepted: 03/17/2014] [Indexed: 12/21/2022] Open
Abstract
Specialized endocrine cells produce and release steroid hormones that govern development, metabolism and reproduction. In order to synthesize steroids, all the genes in the biosynthetic pathway must be coordinately turned on in steroidogenic cells. In Drosophila, the steroid producing endocrine cells are located in the prothoracic gland (PG) that releases the steroid hormone ecdysone. The transcriptional regulatory network that specifies the unique PG specific expression pattern of the ecdysone biosynthetic genes remains unknown. Here, we show that two transcription factors, the POU-domain Ventral veins lacking (Vvl) and the nuclear receptor Knirps (Kni), have essential roles in the PG during larval development. Vvl is highly expressed in the PG during embryogenesis and is enriched in the gland during larval development, suggesting that Vvl might function as a master transcriptional regulator in this tissue. Vvl and Kni bind to PG specific cis-regulatory elements that are required for expression of the ecdysone biosynthetic genes. Knock down of either vvl or kni in the PG results in a larval developmental arrest due to failure in ecdysone production. Furthermore, Vvl and Kni are also required for maintenance of TOR/S6K and prothoracicotropic hormone (PTTH) signaling in the PG, two major pathways that control ecdysone biosynthesis and PG cell growth. We also show that the transcriptional regulator, Molting defective (Mld), controls early biosynthetic pathway steps. Our data show that Vvl and Kni directly regulate ecdysone biosynthesis by transcriptional control of biosynthetic gene expression and indirectly by affecting PTTH and TOR/S6K signaling. This provides new insight into the regulatory network of transcription factors involved in the coordinated regulation of steroidogenic cell specific transcription, and identifies a new function of Vvl and Knirps in endocrine cells during post-embryonic development.
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Affiliation(s)
| | - Morten E. Moeller
- Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Elad Dorry
- Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Tatsuya Komura-Kawa
- Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan
| | - Yoshinori Fujimoto
- Department of Chemistry and Materials Science, Tokyo Institute of Technology, Meguro, Tokyo, Japan
| | - Jesper T. Troelsen
- Department of Science, Systems and Models, Roskilde University, Roskilde, Denmark
| | - Rachel Herder
- Department of Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, Minnesota, United States of America
| | - Michael B. O'Connor
- Department of Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, Minnesota, United States of America
| | - Ryusuke Niwa
- Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan
- PRESTO, JST, Kawaguchi, Saitama, Japan
| | - Kim F. Rewitz
- Department of Biology, University of Copenhagen, Copenhagen, Denmark
- * E-mail:
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68
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Piñeiro C, Lopes CS, Casares F. A conserved transcriptional network regulates lamina development in the Drosophila visual system. Development 2014; 141:2838-47. [PMID: 24924198 DOI: 10.1242/dev.108670] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The visual system of insects is a multilayered structure composed externally by the compound eye and internally by the three ganglia of the optic lobe: lamina, medulla and the lobula complex. The differentiation of lamina neurons depends heavily on Hedgehog (Hh) signaling, which is delivered by the incoming photoreceptor axons, and occurs in a wave-like fashion. Despite the primary role of lamina neurons in visual perception, it is still unclear how these neurons are specified from neuroepithelial (NE) progenitors. Here we show that a homothorax (hth)-eyes absent (eya)-sine oculis (so)-dachshund (dac) gene regulatory cassette is involved in this specification. Lamina neurons differentiate from NE progenitors that express hth, eya and so. One of the first events in the differentiation of lamina neurons is the upregulation of dac expression in response to Hh signaling. We show that this dac upregulation, which marks the transition from NE progenitors into lamina precursors, also requires Eya/So, the expression of which is locked in by mutual feedback. dac expression is crucial for lamina differentiation because it ensures repression of hth, a negative regulator of single-minded, and thus dac allows further lamina neuron differentiation. Therefore, the specification of lamina neurons is controlled by coupling the cell-autonomous hth-eya-so-dac regulatory cassette to Hh signaling.
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Affiliation(s)
- Cristina Piñeiro
- CABD (Andalusian Centre for Developmental Biology), CSIC-UPO-JA, Seville 41013, Spain
| | - Carla S Lopes
- CABD (Andalusian Centre for Developmental Biology), CSIC-UPO-JA, Seville 41013, Spain
| | - Fernando Casares
- CABD (Andalusian Centre for Developmental Biology), CSIC-UPO-JA, Seville 41013, Spain
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69
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Pecot MY, Chen Y, Akin O, Chen Z, Tsui CYK, Zipursky SL. Sequential axon-derived signals couple target survival and layer specificity in the Drosophila visual system. Neuron 2014; 82:320-33. [PMID: 24742459 PMCID: PMC4304384 DOI: 10.1016/j.neuron.2014.02.045] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/21/2014] [Indexed: 12/12/2022]
Abstract
Neural circuit formation relies on interactions between axons and cells within the target field. While it is well established that target-derived signals act on axons to regulate circuit assembly, the extent to which axon-derived signals control circuit formation is not known. In the Drosophila visual system, anterograde signals numerically match R1-R6 photoreceptors with their targets by controlling target proliferation and neuronal differentiation. Here we demonstrate that additional axon-derived signals selectively couple target survival with layer specificity. We show that Jelly belly (Jeb) produced by R1-R6 axons interacts with its receptor, anaplastic lymphoma kinase (Alk), on budding dendrites to control survival of L3 neurons, one of three postsynaptic targets. L3 axons then produce Netrin, which regulates the layer-specific targeting of another neuron within the same circuit. We propose that a cascade of axon-derived signals, regulating diverse cellular processes, provides a strategy for coordinating circuit assembly across different regions of the nervous system.
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Affiliation(s)
- Matthew Y Pecot
- Department of Biological Chemistry, The Howard Hughes Medical Institute, The David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Yi Chen
- Department of Biological Chemistry, The Howard Hughes Medical Institute, The David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Orkun Akin
- Department of Biological Chemistry, The Howard Hughes Medical Institute, The David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Zhenqing Chen
- Department of Biology, New York University, New York, NY 10003, USA
| | - C Y Kimberly Tsui
- Department of Biological Chemistry, The Howard Hughes Medical Institute, The David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - S Lawrence Zipursky
- Department of Biological Chemistry, The Howard Hughes Medical Institute, The David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA.
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70
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Wide-Field Feedback Neurons Dynamically Tune Early Visual Processing. Neuron 2014; 82:887-95. [DOI: 10.1016/j.neuron.2014.04.023] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/28/2014] [Indexed: 11/23/2022]
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71
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Tuthill JC, Nern A, Holtz SL, Rubin GM, Reiser MB. Contributions of the 12 neuron classes in the fly lamina to motion vision. Neuron 2013; 79:128-40. [PMID: 23849200 PMCID: PMC3806040 DOI: 10.1016/j.neuron.2013.05.024] [Citation(s) in RCA: 145] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/10/2013] [Indexed: 10/26/2022]
Abstract
Motion detection is a fundamental neural computation performed by many sensory systems. In the fly, local motion computation is thought to occur within the first two layers of the visual system, the lamina and medulla. We constructed specific genetic driver lines for each of the 12 neuron classes in the lamina. We then depolarized and hyperpolarized each neuron type and quantified fly behavioral responses to a diverse set of motion stimuli. We found that only a small number of lamina output neurons are essential for motion detection, while most neurons serve to sculpt and enhance these feedforward pathways. Two classes of feedback neurons (C2 and C3), and lamina output neurons (L2 and L4), are required for normal detection of directional motion stimuli. Our results reveal a prominent role for feedback and lateral interactions in motion processing and demonstrate that motion-dependent behaviors rely on contributions from nearly all lamina neuron classes.
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Affiliation(s)
- John C Tuthill
- HHMI/Janelia Farm Research Campus, 19700 Helix Drive, Ashburn, VA 20147, USA
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72
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Suzuki T, Kaido M, Takayama R, Sato M. A temporal mechanism that produces neuronal diversity in the Drosophila visual center. Dev Biol 2013; 380:12-24. [DOI: 10.1016/j.ydbio.2013.05.002] [Citation(s) in RCA: 94] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2012] [Revised: 04/21/2013] [Accepted: 05/04/2013] [Indexed: 11/29/2022]
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73
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Temporal patterning of Drosophila medulla neuroblasts controls neural fates. Nature 2013; 498:456-62. [PMID: 23783517 PMCID: PMC3701960 DOI: 10.1038/nature12319] [Citation(s) in RCA: 195] [Impact Index Per Article: 17.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2012] [Accepted: 05/24/2013] [Indexed: 01/17/2023]
Abstract
In the Drosophila optic lobes, the medulla processes visual information coming from inner photoreceptors R7 and R8 and from lamina neurons. It contains ~40,000 neurons belonging to over 70 different types. We describe how precise temporal patterning of neural progenitors generates these different neural types. Five transcription factors--Homothorax, Eyeless, Sloppy-paired, Dichaete and Tailless--are sequentially expressed in a temporal cascade in each of the medulla neuroblasts as they age. Loss of either Eyeless, Sloppy-paired or Dichaete blocks further progression of the temporal sequence. We provide evidence that this temporal sequence in neuroblasts, together with Notch-dependent binary fate choice, controls the diversification of the neuronal progeny. Although a temporal sequence of transcription factors had been identified in Drosophila embryonic neuroblasts, our work illustrates the generality of this strategy, with different sequences of transcription factors being used in different contexts.
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74
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Cis-regulatory complexity within a large non-coding region in the Drosophila genome. PLoS One 2013; 8:e60137. [PMID: 23613719 PMCID: PMC3632565 DOI: 10.1371/journal.pone.0060137] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2012] [Accepted: 02/21/2013] [Indexed: 11/22/2022] Open
Abstract
Analysis of cis-regulatory enhancers has revealed that they consist of clustered blocks of highly conserved sequences. Although most characterized enhancers reside near their target genes, a growing number of studies have shown that enhancers located over 50 kb from their minimal promoter(s) are required for appropriate gene expression and many of these ‘long-range’ enhancers are found in genomic regions that are devoid of identified exons. To gain insight into the complexity of Drosophila cis-regulatory sequences within exon-poor regions, we have undertaken an evolutionary analysis of 39 of these regions located throughout the genome. This survey revealed that within these genomic expanses, clusters of conserved sequence blocks (CSBs) are positioned once every 1.1 kb, on average, and that a typical cluster contains multiple (5 to 30 or more) CSBs that have been maintained for at least 190 My of evolutionary divergence. As an initial step toward assessing the cis-regulatory activity of conserved clusters within gene-free genomic expanses, we have tested the in-vivo enhancer activity of 19 consecutive CSB clusters located in the middle of a 115 kb gene-poor region on the 3rd chromosome. Our studies revealed that each cluster functions independently as a specific spatial/temporal enhancer. In total, the enhancers possess a diversity of regulatory functions, including dynamically activating expression in defined patterns within subsets of cells in discrete regions of the embryo, larvae and/or adult. We also observed that many of the enhancers are multifunctional–that is, they activate expression during multiple developmental stages. By extending these results to the rest of the Drosophila genome, which contains over 70,000 non-coding CSB clusters, we suggest that most function as enhancers.
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75
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Sato M, Suzuki T, Nakai Y. Waves of differentiation in the fly visual system. Dev Biol 2013; 380:1-11. [PMID: 23603492 DOI: 10.1016/j.ydbio.2013.04.007] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2012] [Revised: 04/04/2013] [Accepted: 04/10/2013] [Indexed: 11/19/2022]
Abstract
Sequential progression of differentiation in a tissue or in multiple tissues in a synchronized manner plays important roles in development. Such waves of differentiation are especially important in the development of the Drosophila visual system, which is composed of the retina and the optic lobe of the brain. All of the components of the fly visual system are topographically connected, and each ommatidial unit in the retina corresponds to a columnar unit in the optic lobe, which is composed of lamina, medulla, lobula and lobula plate. In the developing retina, the wave of differentiation follows the morphogenetic furrow, which progresses in a posterior-to-anterior direction. At the same time, differentiation of the lamina progresses in the same direction, behind the lamina furrow. This is not just a coincidence: differentiated photoreceptor neurons in the retina sequentially send axons to the developing lamina and trigger differentiation of lamina neurons to ensure the progression of the lamina furrow just like the furrow in the retina. Similarly, development of the medulla accompanies a wave of differentiation called the proneural wave. Thus, the waves of differentiation play important roles in establishing topographic connections throughout the fly visual system. In this article, we review how neuronal differentiation and connectivity are orchestrated in the fly visual system by multiple waves of differentiation.
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Affiliation(s)
- Makoto Sato
- Brain/Liver Interface Medicine Research Center, Graduate School of Medical Sciences, Lab of Developmental Neurobiology, Kanazawa University, Japan.
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76
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Yu HH, Awasaki T, Schroeder MD, Long F, Yang JS, He Y, Ding P, Kao JC, Wu GYY, Peng H, Myers G, Lee T. Clonal development and organization of the adult Drosophila central brain. Curr Biol 2013; 23:633-43. [PMID: 23541733 DOI: 10.1016/j.cub.2013.02.057] [Citation(s) in RCA: 112] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2012] [Revised: 01/31/2013] [Accepted: 02/27/2013] [Indexed: 10/27/2022]
Abstract
BACKGROUND The insect brain can be divided into neuropils that are formed by neurites of both local and remote origin. The complexity of the interconnections obscures how these neuropils are established and interconnected through development. The Drosophila central brain develops from a fixed number of neuroblasts (NBs) that deposit neurons in regional clusters. RESULTS By determining individual NB clones and pursuing their projections into specific neuropils, we unravel the regional development of the brain neural network. Exhaustive clonal analysis revealed 95 stereotyped neuronal lineages with characteristic cell-body locations and neurite trajectories. Most clones show complex projection patterns, but despite the complexity, neighboring clones often coinnervate the same local neuropil or neuropils and further target a restricted set of distant neuropils. CONCLUSIONS These observations argue for regional clonal development of both neuropils and neuropil connectivity throughout the Drosophila central brain.
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Affiliation(s)
- Hung-Hsiang Yu
- Howard Hughes Medical Institute, Janelia Farm Research Campus, 19700 Helix Drive, Ashburn, VA 20147, USA
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77
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Protection of neuronal diversity at the expense of neuronal numbers during nutrient restriction in the Drosophila visual system. Cell Rep 2013; 3:587-94. [PMID: 23478023 PMCID: PMC3617362 DOI: 10.1016/j.celrep.2013.02.006] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2012] [Revised: 01/22/2013] [Accepted: 02/05/2013] [Indexed: 12/17/2022] Open
Abstract
Systemic signals provided by nutrients and hormones are known to coordinate the growth and proliferation of different organs during development. However, within the brain, it is unclear how these signals influence neural progenitor divisions and neuronal diversity. Here, in the Drosophila visual system, we identify two developmental phases with different sensitivities to dietary nutrients. During early larval stages, nutrients regulate the size of the neural progenitor pool via insulin/PI3K/TOR-dependent symmetric neuroepithelial divisions. During late larval stages, neural proliferation becomes insensitive to dietary nutrients, and the steroid hormone ecdysone acts on Delta/Notch signaling to promote the switch from symmetric mitoses to asymmetric neurogenic divisions. This mechanism accounts for why sustained undernourishment during visual system development restricts neuronal numbers while protecting neuronal diversity. These studies reveal an adaptive mechanism that helps to retain a functional visual system over a range of different brain sizes in the face of suboptimal nutrition.
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78
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Brain-specific-homeobox is required for the specification of neuronal types in the Drosophila optic lobe. Dev Biol 2013; 377:90-9. [PMID: 23454478 DOI: 10.1016/j.ydbio.2013.02.012] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2012] [Revised: 02/15/2013] [Accepted: 02/17/2013] [Indexed: 12/17/2022]
Abstract
The Drosophila optic lobe comprises a wide variety of neurons forming laminar and columnar structures similar to the mammalian brain. The Drosophila optic lobe may provide an excellent model to investigate various processes of brain development. However, it is poorly understood how neuronal specification is regulated in the optic lobe to form a complicated structure. Here we show that the Brain-specific-homeobox (Bsh) protein, which is expressed in the lamina and medulla ganglia, is involved in specifying neuronal identity. Bsh is expressed in L4 and L5 lamina neurons and in Mi1 medulla neurons. Analyses of loss-of-function and gain-of-function clones suggest that Bsh is required and largely sufficient for Mi1 specification in the medulla and L4 specification in the lamina. Additionally, Bsh is at least required for L5 specification. In the absence of Bsh, L5 is transformed into glial cells.
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79
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Hopkins PCR. Neurodegeneration in a Drosophila model for the function of TMCC2, an amyloid protein precursor-interacting and apolipoprotein E-binding protein. PLoS One 2013; 8:e55810. [PMID: 23409049 PMCID: PMC3567013 DOI: 10.1371/journal.pone.0055810] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2012] [Accepted: 01/04/2013] [Indexed: 12/20/2022] Open
Abstract
We previously identified TMCC2 as a protein that interacted differentially with normal versus Alzheimer's disease-risk forms of both apolipoprotein E (apoE) and the amyloid protein precursor (APP). We hypothesized that disrupted function of TMCC2 would affect neurodegeneration. To test this hypothesis, we investigated the Drosophila orthologue of TMCC2, that we have named Dementin. We showed that Dementin interacts genetically both with human APP and its Drosophila orthologue, the APP-like protein (APPL). Ectopic expression of Dementin in Drosophila rescued developmental and behavioral defects caused by expression of human APP. Both a hypomorphic lethal mutation in the dementin gene (dmtn1) and RNAi for Dementin caused the accumulation of fragments derived from APPL. We found that Dementin was required for normal development of the brain, and that glial Dementin was required for development of the Drosophila medulla neuropil. Expression of wild-type Dementin in either the neurons or glia of dmtn1 flies rescued developmental lethality. Adult dmtn1 flies rescued by expression of wild-type Dementin in glia, i.e. whose neurons expressed only dmtn1, showed pathological features resembling early onset Alzheimer's disease, accumulation of abnormal APPL metabolites, synaptic pathology, mis-localized microtubule-binding proteins, neurodegeneration, and early death.
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Affiliation(s)
- Paul C R Hopkins
- Institute of Psychiatry and MRC Centre for Developmental Neurobiology, Kings College London, London, United Kingdom.
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80
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Abstract
Drosophila has recently become a powerful model system to understand the mechanisms of temporal patterning of neural progenitors called neuroblasts (NBs). Two different temporal sequences of transcription factors (TFs) have been found to be sequentially expressed in NBs of two different systems: the Hunchback, Krüppel, Pdm1/Pdm2, Castor, and Grainyhead sequence in the Drosophila ventral nerve cord; and the Homothorax, Klumpfuss, Eyeless, Sloppy-paired, Dichaete, and Tailless sequence that patterns medulla NBs. In addition, the intermediate neural progenitors of type II NB lineages are patterned by a different sequence: Dichaete, Grainyhead, and Eyeless. These three examples suggest that temporal patterning of neural precursors by sequences of TFs is a common theme to generate neural diversity. Cross-regulations, including negative feedback regulation and positive feedforward regulation among the temporal factors, can facilitate the progression of the sequence. However, there are many remaining questions to understand the mechanism of temporal transitions. The temporal sequence progression is intimately linked to the progressive restriction of NB competence, and eventually determines the end of neurogenesis. Temporal identity has to be integrated with spatial identity information, as well as with the Notch-dependent binary fate choices, in order to generate specific neuron fates.
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Affiliation(s)
- Xin Li
- Department of Biology, New York University, New York, New York, USA
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81
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Kim WJ, Jan LY, Jan YN. Contribution of visual and circadian neural circuits to memory for prolonged mating induced by rivals. Nat Neurosci 2012; 15:876-83. [PMID: 22561453 PMCID: PMC3417086 DOI: 10.1038/nn.3104] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2012] [Accepted: 04/04/2012] [Indexed: 01/27/2023]
Abstract
Rival exposure causes Drosophila melanogaster males to prolong mating. Longer-Mating-Duration (LMD) may enhance reproductive success, but its underlying mechanism is currently unknown. Here we report that LMD is context-dependent and can be induced solely via visual stimuli. We further show that LMD involves neural circuits important for visual memory, including central neurons in the ellipsoid body but not the mushroom bodies or the fan-shaped bodies, and may rely on the rival exposure memory lasting several hours. LMD is affected by a subset of learning and memory mutants. LMD depends on the circadian clock genes timeless and period but not Clock or cycle, and persists in many arrhythmic conditions. Moreover, LMD critically depends on a subset of pigment dispersing factor (PDF) neurons rather than the entire circadian neural circuit. Our study thus delineates parts of the molecular and cellular basis for LMD – a plastic social behavior elicited by visual cues.
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Affiliation(s)
- Woo Jae Kim
- Howard Hughes Medical Institute, Departments of Physiology, Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA, USA
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82
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Togane Y, Ayukawa R, Hara Y, Akagawa H, Iwabuchi K, Tsujimura H. Spatio-temporal pattern of programmed cell death in the developing Drosophila optic lobe. Dev Growth Differ 2012; 54:503-18. [PMID: 22587328 DOI: 10.1111/j.1440-169x.2012.01340.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
A large number of cells die via programmed cell death during the normal development of the Drosophila optic lobe. In this study, we report the precise spatial and temporal pattern of cell death in this organ. Cell death in the developing optic lobe occurs in two distinct phases. The first phase extends from the start of metamorphosis to the mid-pupal stage. During this phase, a large number of cells die in the optic lobe as a whole, with a peak of cell death at an early pupal stage in the lamina and medulla cortices and the region of the T2/T3/C neurons, and a smaller number of dead cells observed in the lobula plate cortex. The second phase extends from the mid-pupal stage to eclosion. Throughout this period, a small number of dying cells can be observed, with a small peak at a late pupal stage. Most of the dying cells are neurons. During the first phase, dying cells are distributed in specific patterns in cortices. The lamina cortex contains two distinct clusters of dying cells; the medulla cortex, four clusters; the lobula plate cortex, one cluster; and the region of the T2/T3/C neurons, one cluster. Many of the clusters maintain their distinct positions in the optic lobe but others extend the region they cover during development. The presence of distinct clusters of dying cells at different phases suggests that distinct mechanisms control cell death during different stages of optic lobe development in Drosophila.
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Affiliation(s)
- Yu Togane
- Developmental Biology, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-si, Tokyo, 183-8509, Japan
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83
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Osumi-Sutherland D, Reeve S, Mungall CJ, Neuhaus F, Ruttenberg A, Jefferis GSXE, Armstrong JD. A strategy for building neuroanatomy ontologies. Bioinformatics 2012; 28:1262-9. [PMID: 22402613 DOI: 10.1093/bioinformatics/bts113] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
MOTIVATION Advancing our understanding of how nervous systems work will require the ability to store and annotate 3D anatomical datasets, recording morphology, partonomy and connectivity at multiple levels of granularity from subcellular to gross anatomy. It will also require the ability to integrate this data with other data-types including functional, genetic and electrophysiological data. The web ontology language OWL2 provides the means to solve many of these problems. Using it, one can rigorously define and relate classes of anatomical structure using multiple criteria. The resulting classes can be used to annotate datasets recording, for example, gene expression or electrophysiology. Reasoning software can be used to automate classification and error checking and to construct and answer sophisticated combinatorial queries. But for such queries to give consistent and biologically meaningful results, it is important that both classes and the terms (relations) used to relate them are carefully defined. RESULTS We formally define a set of relations for recording the spatial and connectivity relationships of neuron classes and brain regions in a broad range of species, from vertebrates to arthropods. We illustrate the utility of our approach via its application in the ontology that drives the Virtual Fly Brain web resource. AVAILABILITY AND IMPLEMENTATION The relations we define are available from http://purl.obolibrary.org/obo/ro.owl. They are used in the Drosophila anatomy ontology (http://purl.obolibrary.org/obo/fbbt/2011-09-06/), which drives the web resource http://www.virtualflybrain.org
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Song E, de Bivort B, Dan C, Kunes S. Determinants of the Drosophila odorant receptor pattern. Dev Cell 2012; 22:363-76. [PMID: 22340498 DOI: 10.1016/j.devcel.2011.12.015] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2011] [Revised: 10/24/2011] [Accepted: 12/20/2011] [Indexed: 02/04/2023]
Abstract
In most olfactory systems studied to date, neurons that express the same odorant receptor (Or) gene are scattered across sensory epithelia, intermingled with neurons that express different Or genes. In Drosophila, olfactory sensilla that express the same Or gene are dispersed on the antenna and the maxillary palp. Here we show that Or identity is specified in a spatially stereotyped pattern by the cell-autonomous activity of the transcriptional regulators Engrailed and Dachshund. Olfactory sensilla then become highly motile and disperse beneath the epidermis. Thus, positional information and cell motility underlie the dispersed patterns of Drosophila Or gene expression.
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Affiliation(s)
- Erin Song
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138, USA
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85
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Ando M, Totani Y, Walldorf U, Furukubo-Tokunaga K. TALE-class homeodomain transcription factors, homothorax and extradenticle, control dendritic and axonal targeting of olfactory projection neurons in the Drosophila brain. Dev Biol 2011; 358:122-36. [PMID: 21801717 DOI: 10.1016/j.ydbio.2011.07.018] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2010] [Revised: 07/06/2011] [Accepted: 07/13/2011] [Indexed: 12/31/2022]
Abstract
Precise neuronal connectivity in the nervous system depends on specific axonal and dendritic targeting of individual neurons. In the Drosophila brain, olfactory projection neurons convey odor information from the antennal lobe to higher order brain centers such as the mushroom body and the lateral horn. Here, we show that Homothorax (Hth), a TALE-class homeodomain transcription factor, is expressed in many of the antennal lobe neurons including projection neurons and local interneurons. In addition, HTH is expressed in the progenitors of the olfactory projection neurons, and the activity of hth is required for the generation of the lateral but not for the anterodorsal and ventral lineages. MARCM analyses show that the hth is essential for correct dendritic targeting of projection neurons in the antennal lobe. Moreover, the activity of hth is required for axonal fasciculation, correct routing and terminal branching of the projection neurons. We also show that another TALE-class homeodomain protein, Extradenticle (Exd), is required for the dendritic and axonal development of projection neurons. Mutation of exd causes projection neuron defects that are reminiscent of the phenotypes caused by the loss of the hth activity. Double immunostaining experiments show that Hth and Exd are coexpressed in olfactory projection neurons and their progenitors, and that the expressions of Hth and Exd require the activity of each other gene. These results thus demonstrate the functional importance of the TALE-class homeodomain proteins in cell-type specification and precise wiring of the Drosophila olfactory network.
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Affiliation(s)
- Mai Ando
- Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba 305-8572, Japan
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86
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Zhu Z, Bhat KM. The Hem protein mediates neuronal migration by inhibiting WAVE degradation and functions opposite of Abelson tyrosine kinase. Dev Biol 2011; 357:283-94. [PMID: 21726548 DOI: 10.1016/j.ydbio.2011.06.025] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2011] [Revised: 06/17/2011] [Accepted: 06/18/2011] [Indexed: 10/18/2022]
Abstract
In the nervous system, neurons form in different regions, then they migrate and occupy specific positions. We have previously shown that RP2/sib, a well-studied neuronal pair in the Drosophila ventral nerve cord (VNC), has a complex migration route. Here, we show that the Hem protein, via the WAVE complex, regulates migration of GMC-1 and its progeny RP2 neuron. In Hem or WAVE mutants, RP2 neuron either abnormally migrates, crossing the midline from one hemisegment to the contralateral hemisegment, or does not migrate at al and fail to send out its axon projection. We report that Hem regulates neuronal migration through stabilizing WAVE. Since Hem and WAVE normally form a complex, our data argues that in the absence of Hem, WAVE, which is presumably no longer in a complex, becomes susceptible to degradation. We also find that Abelson tyrosine kinase affects RP2 migration in a similar manner as Hem and WAVE, and appears to operate via WAVE. However, while Abl negatively regulates the levels of WAVE, it regulates migration via regulating the activity of WAVE. Our results also show that during the degradation of WAVE, Hem function is opposite to that of and downstream of Abl.
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Affiliation(s)
- Zengrong Zhu
- Department of Neuroscience and Cell Biology, University of Texas Medical Branch School of Medicine, Galveston, TX, 77598, USA
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Candidate glutamatergic neurons in the visual system of Drosophila. PLoS One 2011; 6:e19472. [PMID: 21573163 PMCID: PMC3088675 DOI: 10.1371/journal.pone.0019472] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2011] [Accepted: 04/03/2011] [Indexed: 01/17/2023] Open
Abstract
The visual system of Drosophila contains approximately 60,000 neurons that are organized in parallel, retinotopically arranged columns. A large number of these neurons have been characterized in great anatomical detail. However, studies providing direct evidence for synaptic signaling and the neurotransmitter used by individual neurons are relatively sparse. Here we present a first layout of neurons in the Drosophila visual system that likely release glutamate as their major neurotransmitter. We identified 33 different types of neurons of the lamina, medulla, lobula and lobula plate. Based on the previous Golgi-staining analysis, the identified neurons are further classified into 16 major subgroups representing lamina monopolar (L), transmedullary (Tm), transmedullary Y (TmY), Y, medulla intrinsic (Mi, Mt, Pm, Dm, Mi Am), bushy T (T), translobula plate (Tlp), lobula intrinsic (Lcn, Lt, Li), lobula plate tangential (LPTCs) and lobula plate intrinsic (LPi) cell types. In addition, we found 11 cell types that were not described by the previous Golgi analysis. This classification of candidate glutamatergic neurons fosters the future neurogenetic dissection of information processing in circuits of the fly visual system.
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